The present invention relates generally to switches and, more particularly, to an apparatus and method for remotely controlling the current to at least one load.
In many industries today, such as the avionics and automotive industries, in order to protect complex and costly electrical components, systems and subsystems, electrical power systems powering these components, systems and subsystems employ circuit breakers and relays. Typically, circuit breakers interrupt the current in an electric circuit, sometimes referred to as tripping the circuit breaker, when the current through the circuit becomes higher than that allowed by the circuit breaker. Conventional circuit breakers are typically rated for a specific current level that depends upon the components in the circuit and their current tolerances. When the current through the circuit breaker exceeds the rated current level, the circuit breaker trips and interrupts the current in the circuit. In one type of conventional circuit breaker, a mechanical circuit breaker, when enough current runs through the circuit to trip the circuit breaker, a pair of contacts that are normally in contact in order to conduct current through the circuit breaker and the rest of the circuit are separated, such as by preloaded springs, thus breaking the circuit.
In addition to circuit breakers, many industries today employ relays to control the flow of current to components, systems and/or subsystems. Conventional relays are electromechanical switches that are operated by a flow of current in one circuit which controls the flow of current in another circuit. One basic conventional relay consists of an electromagnet with a soft iron bar, or armature, disposed close to the electromagnet. A movable contact is connected to the armature such that the contact is held in a normal position by a spring, or similar device. To actuate the relay, the electromagnet is energized, such as by passing a current through it, thereby exerting a force on the armature which, in turn, causes the contact to overcome the pull of the spring and move so as to either complete or break the circuit. When the electromagnet is de-energized, such as by halting the current flow through the electromagnet, the contact returns to its original, normal position.
While conventional circuit breakers and relays are used in many power systems, they pose some problems. Many conventional circuit breakers and relays allow excessive current to flow when the contacts open and close the circuit. In these circuit breakers and relays, the excessive current flow results in an electric arc that forms at the contacts, which typically erodes the contacts and can, in some instances, weld them closed. The electric arc can also result in the contacts becoming carbonized, thereby not allowing the contacts surfaces to adequately conduct electrical current. Additionally, the presence of the electric arc can add unnecessary danger to electrical devices and people around such devices in instances in which combustible gases have collected around the circuit breaker or relay.
To allow access to conventional circuit breakers and relays, in many conventional power systems, they are placed on centrally located panels in areas that are typically distant from the components, systems and/or subsystems being protected and/or controlled. This results in long cable assemblies that extend between the circuit breakers and/or relays and the components, systems and/or subsystems being protected and/or controlled. The length of the cables can additionally result in parasitic impedance, which can cause a loss of power to the system, and can increase system noise. This results in lowering the efficiency of the power system. Additionally, longer cables also increase the weight of the power system, because, as stated, the cables must reach extended lengths to control the various components and/or subsystems.
In addition to lower reliability and increased weight of conventional mechanical circuit breakers and relays, conventional mechanical circuit breakers suffer from limitations due to their material characteristics. Most of these conventional circuit breakers cannot be adjusted for different requirements without replacing the entire circuit breaker. For example, if a mechanical circuit breaker is rated for a ten amp trip and is attached to a circuit containing a component, system or subsystem rated for five amps, the ten amp rated circuit breaker would need to be replaced with a five amp rated circuit breaker to provide over-current protection for the five amp rated component, system or subsystem. Additionally, conventional mechanical circuit breakers do not allow for adjustments accounting for power-up inrush current, or adjustments in trip voltages accounting for fluctuations in the voltage drop across a mechanical circuit breaker due to temperature changes in the circuit breaker.
In light of the foregoing background, the present invention provides a programmable controller capable of interfacing with a remote master controller, where the programmable controller is capable of controlling an input current to at least one load, such as a component and/or subsystem that is proximate the programmable controller. The programmable controller of the present invention includes at least one solid-state switch capable of limiting the input current to the loads to a predetermined value at or below the maximum current rating of the solid-state switch. In one embodiment, each solid state switch includes a switching element electrically connected to a respective load to monitor and control the input current and voltage levels to the respective load, and a drive element to provide the input current to the respective load. In this embodiment, the switching element controls the input current provided by the drive element. Using a solid-state switch, such as a metal oxide semiconductor field-effect transistor (MOSFET) or an integrated gate bipolar transistor (IGBT), the programmable controller eliminates the mechanical contacts of conventional circuit breakers and relays, thus eliminating the erosion and associated problems with such contacts.
The programmable controller also includes at least one measuring element for measuring at least one parameter associated with the loads and the solid-state switches. For example, in various embodiments, the programmable controller can measure the current through the solid-state switches, the current through and voltage drop across the loads and the temperature at or around the solid-state switches. Using these parameters, the programmable controller can protect the loads and solid-state switches from damage, such as that caused by over current, over voltage, under voltage, over temperature and under temperature conditions.
The programmable controller of the present invention also includes a processing element, such as a microcontroller, electrically connected to the solid-state switches and measuring elements. The processing element is capable of controlling the solid-state switches. For example, the processing element can control the respective switches in an on mode where the solid-state switch permits a respective load to receive the input current, or an off mode where the solid-state switch prevents the respective load from receiving the input current.
In one embodiment, the programmable controller can further include a memory device electrically connected to the processing element for storing information relative to the switches and/or loads in addition to user preferences and built-in-test information. To backup the operation of the processing element, in another embodiment, the programmable controller further includes a monitoring element electrically connected to the processing element and the solid-state switches. In instances when the processing element fails to function properly by failing to control the solid-state switches, the monitoring element is capable of controlling the solid-state switches to alter the input current to a predefined level.
By using a processing element to control the solid-state switches and measuring elements, the programmable controller of the present invention provides flexibility in power control not available in conventional circuit breakers or relays. Using the processing element, and placing it near the components and/or subsystems, the programmable controller reduces the amount of cabling required in electrical devices employing conventional circuit breakers and/or relays, and overcomes the material limitations of conventional circuit breakers and relays. By reducing the lengths of the cabling required by the power system, the programmable controller improves the efficiency by reducing the parasitic impedance within the cabling. Reducing the cabling also reduces the weight of the electrical devices.
Using a processing element also allows the programmable controller of the present invention to overcome the material limitations of conventional circuit breakers and relays. In the previous example, if a five amp rated load is connected to a conventional ten amp rated circuit breaker, the circuit breaker would need to be replaced with a new, five amp rated circuit breaker to protect the load. But using the programmable controller of the present invention, the processing element need only be configured for the particular load, such as the current requirement of the load, and can be reconfigured (or reprogrammed) for a different load. For example, the processing element can be programmed and reprogrammed depending on such load characteristics as current, voltage and temperature ratings of the load. The processing element can also be programmed and reprogrammed depending upon characteristics of the solid-state switch, thereby allowing for even greater flexibility. Additionally, using one processing element to control multiple loads, allows one programmable controller to be independently configured for multiple, different loads, without using multiple, different types of conventional circuit breakers.
In embodiments including a switching element and a drive element, the switching element can have a maximum current rating, and each solid-state switch can further include a switch-protection element electrically connected to the switching element and the drive element. The switch-protection element protects the solid-state switch from over-current by sensing an actual current through the switching element and controlling the input current to loads depending upon the actual current and the maximum current rating. For example, the switch protection element can control the drive element to provide the input current to a respective load such that the actual current through the switching element is no more than the maximum current rating of the respective switching element. Additionally, to allow for an inrush of current through the switching element when it is initialized, the switch-protection element can, alternatively or additionally, control the drive element to wait to control the actual current through the switching element until after a predefined period of time or can be configured to control the current in different manners at different times or in different modes of operation.
The present invention also provides a system of remotely controlling at least one load, including a master controller for controlling an input current to the at least one load, and at least one slave controller situated remote from the master controller and proximate the loads, where the slave controller is electrically connected between the master controller and the load. The slave controller includes the solid-state switches, the measuring elements and the processing element. And in one embodiment, the system further includes a user interface electrically connected to the master controller. The user interface allows a user to control the input current to the loads.
In operation, the processing element is configured based upon at least one characteristic, such as a current rating of each load, a voltage rating of each load, a maximum current rating of each switch and/or a temperature rating of each switch. Then the processing element monitors, such as via the measuring elements, at least one parameter associated with each switch and respective load, such as the input current to the load, a voltage drop across the load, the input current through the switch and/or a temperature of the switch. Then the processing element determines a condition of each switch and respective load depending upon at least one of the at least one characteristic and the at least one parameter. Then, the processing element operates each switch to control the input current to each load, such as by operating each switch in the on mode or placing each switch in the off mode, where the mode selected depends upon the condition of the respective load and switch.
As previously stated, the programmable controller can protect the loads and solid-state switches from damage caused from over current, over voltage, under voltage, over temperature and under temperature conditions. To protect each switch for instantaneous over current, in embodiments including a switch-protection element, the switch-protection element can determine the condition of each switch based upon the maximum current rating of the switch and the input current through the switch, and thereafter control the switch. For example, the switch-protection element can operate the switch in the on mode when the input current through the switch is no more than the maximum current rating for that switch, and place the switch in the off mode when the input current through the switch exceeds the maximum current rating. As previously stated, to allow for inrushes of current, the switch protection element can, alternatively or additionally, wait a predefined period of time to allow the inrush of current to settle before checking to determine if the switch should be placed in the off mode.
In protecting each load from over currents, the processing element of the programmable controller can determine the condition of each load based upon the current rating of the load and the input current to the load. For example, in one embodiment, when the input current to a respective load is not more than a predetermined value relative to the current rating of the load, the processing element operates the respective switch in the on mode. But, on the other hand, when the input current to the respective load exceeds the predetermined value, the processing element operates the switch by placing it in the off mode. In another embodiment, the processing element can additionally consider an amount of time the load has received the input current when determining the condition of the respective load. And in a further embodiment, the processing element can account for previous current stresses on the switch and/or the load (e.g., when the input current exceeds the predetermined value) by maintaining a count that increases as the input current remains above the predetermined value, and that decreases once the input current falls below the predetermined value.
To protect each load from over voltage conditions, in one embodiment, the processing element determines the condition of each load based upon the voltage rating of the load and the voltage drop across the load. If, for example, the voltage drop across a respective load is no more than a predetermined value relative to the voltage rating of the load, the processing element operates the respective switch in the on mode. If the voltage drop exceeds the predetermined value, however, the processing element operates the switch by placing it in the off mode. To protect each load from under voltage conditions, the processing element can operate the respective switch in the on mode when the voltage drop across a respective load is no less than the predetermined value and placing it in the off mode when the voltage drop is below the predetermined value.
In one advantageous embodiment, the processing element protects each switch from over heating by first determining the condition of each switch based upon the temperature rating of the switch and the temperature at or around the switch. If, for example, the temperature of the switch is no more than a predetermined value relative to the respective temperature rating, the processing element operates the respective switch in the on mode; however, if the temperature exceeds the predetermined value, the processing element places the respective switch in the off mode. To protect each switch from under temperature conditions, the processing element monitors each switch for such a condition and operates the switch accordingly. For example, when the temperature of the respective solid-state switch is no less than the predetermined value, the processing element operates the respective switch in the on mode. But, when the temperature is below the predetermined value, the processing element places the switch in the off mode.
The present invention therefore provides a programmable controller capable of interfacing with a remote master controller, where the programmable controller is capable of controlling the input current to at least one load. The programmable controller provides several advantages over conventional circuit breakers and relays by employing a solid-state switch and a processing element. By including solid-state switches, the programmable controller eliminates the problematic mechanical contacts of conventional circuit breakers and relays. By using a processing element, the programmable controller provides flexibility in power control not available in conventional circuit breakers or relays. The programmable controller can concurrently measure and monitor the loads and switches for the current through the loads and/or switches, the voltage drop across the loads and/or the temperature of the switches. Using a processing element, and by placing it near the loads, allows the programmable controller to reduce the amount of cabling required for power systems employing the present invention which, in turn, reduces parasitic impedance in the cabling and weight of the system. Also, the processing element allows the programmable controller of the present invention to overcome the material limitations of conventional circuit breakers and relays, and operate multiple, different types of loads.